One standard for mobile telephone communications is the Global System for Mobile Communications (GSM) standard. The GSM standard covers four large frequency bands and requires the mobile telephone to operate between 14 and 16 specific power levels in each of the frequency bands. With an open-loop transmitter, a large number of frequency bands, and so many power levels, individually calibrating the output power of the mobile telephone for each power level within each frequency band is costly. Accordingly, it is desirable to use a power calibration technique that uses a small number of measurements to calibrate the output power of the mobile telephone for each frequency band.
Many GSM mobile telephones use an analog control voltage to control the gain of a power amplifier in the transmit chain of the mobile telephone, and thus the output power. Historically, an output power versus control voltage characteristic of the power amplifier is assumed to be linear. Thus, for each frequency band, the output power is calibrated by measuring the output power at two power levels and using a first order curve fit to predict the output power versus control voltage characteristic of the power amplifier for all output power levels. The linear assumption introduces errors in output power accuracy that may be considered unacceptable. Thus, there remains a need for a more accurate power calibration technique that uses a small number of measurements to calibrate the output power of the mobile telephone for each frequency band.